1. Field of the Invention
This invention relates to a webbing guiding structure for an automobile seat belt system, and specifically to a reinforced structure of a slide rail and a movable runner for a passive seat belt system.
2. Description of the Related Art
In conventional seat belt systems, slidable shoes for movable runners had possibility inherent to their structures that a load would be concentrated on outer edge portions of the slidable shoes.
As illustrated by way of example in FIG. 4, slide surfaces 41 formed on upper walls of paired lips 43, which in combination define a gap 42 of a slide rail 40, both lie in a plane perpendicular to an imaginary central axis of the slide rail and overhanging side surfaces 51 of a plastic-made slidable shoe 50 of a movable runner 60 also lie in a plane perpendicular to an imaginary central axis of the slidable shoe 50. The overhanging side surfaces 51 of the slidable shoe 50 of the movable runner 60 on and along the corresponding slide surfaces 41 of the lips 43 of the slide rail 40. The above rail/runner structure, namely, webbing guiding structure does not develop problems so long as pulling, namely, downward forces are applied to the movable runner 60 along the imaginary central axis of the slide rail 40.
If a pulling force F is applied to the movable runner 60 by way of a webbing (not shown) connected to the movable runner 60 in the event of an emergency of an associated automobile, the movable runner 60 is caused to turn counterclockwise approximately about a point X so that the overhanging side surfaces 51 are brought into contact at a certain angle with their corresponding slide surfaces 41. As indicated by arrow b in FIG. 4, a left-hand edge portion of the left-hand overhanging side surface 51 undergoes substantially point-to-point contact with the left-hand slide surface 41 of the slide rail 40. This is attributed to the rail/runner structure that the slide surfaces 41 lie in the plane perpendicular to the imaginary central axis of the slide rail 40 and the overhanging side surfaces 51 lie in the plane perpendicular to the imaginary central axis of the slidable shoe 50.
As is apparent from FIG. 5, the movable runner 60 is constructed of an iron plate 53 connected to an unillustrated webbing, a pair of strength members 56 arranged on both sides of the iron plate 53 and united together with the iron plate 53 by pins 55. The plastic-made slidable shoe 50 covers the iron plate 53, strength members 56 and pins 55. When a situation similar to point-to-point contact arises between the left-hand edge portion of the left-hand overhanging side surface 51 and the corresponding slide surface 41 of the slide rail 40 as illustrated in FIG. 4, a large load is concentrated on a left-hand edge portion of the slidable shoe 50 as viewed in FIG. 5 so that the large load is not borne or supported by the left-hand strength member 56 and the slidable shoe 50 is hence sheared off there.
In addition, a shear force and a large bending moment are applied to each pin 55 at points proximal to both sides of the iron plate 53. The strength of the movable runner 60 must hence be enhanced structurally in its entirety, resulting in a drawback that the conventional movable runner 60 unavoidably becomes heavy in weight and large in dimensions.